HEAT-INDUCIBLE EXPRESSION OF FLP GENE IN MAIZE CELLS

The soybean heat-shock gene promoter (Gmhsp 17.5-E) has been used to d irect expression of gusA and FLP genes in maize cells. At inducible te mperatures, in transient expression assays, gusA gene expression contr olled by the heat-shock promoter is about 10-fold higher than the expr ession directed by the CaMV 35S promoter. The Gmhsp 17.5-E promoter pr eserves its regulatory functions in heterologous maize cells after ran dom integration into genomic DNA. Heat-shock inducible expression of t he FLP gene was investigated by co transformation of the FLP expressio n vector (pHsFLP) and a recombination test vector (pUFNeo-FmG) into ma ize protoplasts. Go-transformed protoplasts were incubated at 42 degre es C for 2 h. This treatment induced recombination of 20-25% of the av ailable FRT sites in transient assays. As a result of heat-shock treat ment of stably co-transformed maize cells, activation of gusA gene exp ression and an associated decrease or elimination of NPT-II activity i n transgenic maize lines was observed. Molecular evidence was obtained of the expected DNA excision process catalyzed by the FLP protein in maize transgenic cells. Thus, the experiments presented in this paper indicate that the FLP protein can recognize and subsequently recombine the FRT target sites that had integrated into plant genomic DNA, and that regulated expression of the FLP gene is possible in maize cells u sing the soybean heat-shock promoter.